Entwicklung des Exjection Verfahrens für Kautschuke unter Berücksichtigung des viskoelastischen Materialverhaltens

Translated title of the contribution: Development of the Exjection process for rubbers taking into account the viscoelastic material behavior

Sebastian Stieger

    Research output: ThesisDoctoral Thesis


    Large dimensional 3D-shaped elastomer seals are produced in time consuming processes (compression molding, turning of semi-finished vulcanisates), as alternative technologies like injection molding or extrusion are suffering from major draw-backs. This thesis transfers the patented Exjection®-technology to rubber processing. It combines the advantages of injection molding (3D-shaped parts with high dimensional accuracy) and extrusion (continuous production) by using a movable tool slider as a cavity. Consequently, the length of the manufactured part is neither restricted by the platen size nor by the pressure limit of the injection molding machine any longer. To carry out systematic experiments, a test mold was designed first. Good-parts may only be produced with closed cavity (no endless rubber injection molding) and injection times less than the scorch time of the material. Furthermore, a 2²-factorial design of experiments (DoE) analyses the influence of the volumetric flow rate and the vulcanization time on various part properties (compression set, tensile strength, elongation at break). Compared to compression molded plates, standard deviations are higher (different specimen preparation), but mean values are similar. Furthermore, a two-stage simulation approach, which separates the gating system from the actual mold filling process, aims to virtually reproduce RubExject. The simulation setup contains a viscous material model taking into account the pressure dependency of the viscosity. While simulation results match pressure drops of the gating system well (mean deviation HNBR < 6.5 %), the complex filling behavior of the HNBR rubber compound is not represented correctly. A comprehensive literature research identifies the integral viscoelastic and time dependent Kaye‐Bernstein–Kearsley–Zapas (KBKZ) model as a promising alternative approach. For unfilled polymer melts, it correctly predicts entropy-elastic flow phenomena such as die swell or inlet vortices, as well as the pressure losses in contraction and capillary flows. Additionally, this thesis addresses the open research question whether the integral constitutive equation of the KBKZ type is suitable for describing highly filled polymer systems as well. Therefore, exhaustive rheological testing of an unfilled HNBR rubber gum and two highly carbon black filled rubber (HNBR and NBR) compounds was carried out. Comparing CFD simulation results to measured data, only the pressure drop of the unfilled rubber gum was predicted correctly. Adding fillers to a polymer matrix increases the linear viscoelastic moduli, but decreases entropy-elastic flow phenomena. The KBKZ model is not able to reflect this kind of material behavior in its current mathematical formulation. To ensure its applicability to highly filled polymer systems 1) a dependency on the effective filler volume as well as 2) a (visco)plastic term must be added.
    Translated title of the contributionDevelopment of the Exjection process for rubbers taking into account the viscoelastic material behavior
    Original languageGerman
    Awarding Institution
    • Montanuniversität
    • Wießner, Sven, Assessor B (external), External person
    • Friesenbichler, Walter, Supervisor (internal)
    • Pinter, Gerald Gerhard, Co-Supervisor (internal)
    • Holzer, Clemens, Assessor A (internal)
    Publication statusPublished - 2020

    Bibliographical note

    embargoed until 27-10-2023


    • Rubber injection molding
    • Exjection
    • Rheology
    • Viscoelastic modelling
    • K-BKZ model

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